Filament rotor structures

ABSTRACT

A rotational energy storage device comprising in its basic form a rotor or &#39;&#39;&#39;&#39;flywheel&#39;&#39;&#39;&#39; structure constructed of straight anisotropic filamentary members, the members being disposed in substantially parallel relation to the major stress component acting on the structure. Each filamentary member is essentially loaded along its longitudinal axis, thereby permitting maximum utilization of high strength-to-density uniaxial properties of the member.

United States Patent Rabenhorst [54] FILAMENT ROTOR STRUCTURES [72] inventor: David W. Rabenhorst, Silver Spring, Md.

[73] Assignee: The Johns Hopkins University, Baltimore,

[22] Filed: July 31,1970

[2]] Appl.No.: 60,047

[52] [1.8. Pl 74/572, 161/60 [51] Int. Cl. l6c 15/00 [58] Field of Search ..74/572; 156/296, 297; 161/168, l6l/l72, 60, 239, 247; 15/179, 180, 181, 182, 186,

[56] References Cited UNITED STATES PATENTS 2,621,140 12/1952 Bitterli et a1. ..161/60 X 1,567,574 12/1925 Clay 1,703,510 2/1929 Charette ..15/l81 X 1 June 27, 1972 1,764,651 6/1930 Simmons 15/ l 98 X 1,961,926 6/1934 Gerhardt ....15/l98 3,071,795 1/1963 Hartz et a1... ....l5/l98 3,372,220 3/1968 Stingley 15/179 X 3,296,886 1/ 1967 Reinhart, Jr. ..74/572 3,496,799 2/ 1970 Call ..74/572 Primary Examiner-William F. O'Dea Assistant Examiner-F. D. Shoemaker Attorney-John S. Lacey [5 7] ABSTRACT A rotational energy storage device comprising in its basic form a rotor or flywheeP structure constructed of straight anisotropic filamentary members, the members being disposed in substantially parallel relation to the major stress component acting on the structure. Each filamentary member is essentially loaded along its longitudinal axis, thereby permitting maximum utilization of high strength-to-density uniaxial properties of the member.

26 Claims, 24 Drawing Figures P'A'TENTEDJm'! I972 3,672,241

sum o1ur11 INVENTOR. DAVID W. RABENHORST P'ATENTEIIJum nan sum 02 or 11 INVENTOR. DAVID W. RABENHORST BYawz- P'A'TENTEDJum 1972 saw as ur 11 INVENTOR. I DAVID W. RABENHORST FIG. 5b

PhTENTEnduxzvmz 3.672.241 saw on nr 11 INVENTOR.

. RABENHORST INVENTOR.

DAVID W. RAB NHORST BY 912. 1 m

P'A'TENTEDJum m2 3. 672 241 sum 06 or 11 INVENTOR. DAVID W. RAB ENHORST BY 21% i 6&

PKTENTEDJm'! 1972 saw 08 0F 11' INVENTOR.

DAVID W. RABENHORST BY 8% J flu? PATENIEDJum m2 sum 10 or 11' INVENTOR. BYDAVID W. RABENHORST P'A'TE'NTEDJum 1972 snw 11 or 11 FIG. /5b

FIG. I50

INVENTOR W. RABENHORST BY 2% 4 06M,

FILAMENT ROTOR STRUCTURES The invention herein described was made in the course of or under a contract or subcontract thereunder, with the Department of the Navy.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to energy storage devices, such as flywheels, and particularly to performance-optimized highspeed rotary structures. Application of the invention ranges from use as the sole power source of a quiet, pollution free urban vehicle to powered portable hand tools.

2. Description of the prior art The flywheel has been used for centuries as an efficient energy storage device. Since the flywheel is an inertial device governed by the laws of kinetic energy, maximum per formance is attained at maximum speed, the performance being generally quadrupled with a two-fold increase in speed. The speed of the rotating body, however, cannot be increased beyond its bursting limit. In the prior art, three general flywheel configurations are predominant, namely, the flat disc type characterized by smooth parallel surfaces between the hub and the periphery; the rim type having a massive peripheral portion secured to the hub by spokes or a solid wheel portion; and the more recently developed optimized disc.

Materials used to fabricate high-energy flywheels must have large specific strengths (strength/density) to enable the structure to be rotated at a high velocity. High strength steel has or dinarily been chosen as flywheel material. However, the strength/density ratio of an isotropic steel structure is substantially less than that obtainable with modern anisotropic filamentary materials. High strength filaments typically exhibit substantially greater strength-to-density characteristics over the best isotropic materials, such as steel or titanium. Only a small portion of this strength advantage can be used in the prior art flywheels due to the inherent isotropic stresses in these structures. In the rim type flywheel, stresses normal to the wound filaments exist at all locations other than the outer edge. Additionally, the problem of attachment of the rim to the hub, requiring additional weight, has been a principal factor inhibiting further development of this flywheel structure.

The present rotational energy storage device features flywheel rotor structures capable of substantial improvement in useable energy density, primarily because a much higher percentage of filament specific strength is useable. Characteristic of the present rotor structure is the use of straight anisotropic filamentary material arranged in the structure so as to permit maximum utilization of the filament strength in its axial direction.

The significance of the present energy storage device is best understood-by its application to the urban vehicle. Although flywheels have been previously used in short-range vehicles, such as in the Swiss Oerlikon bus and in the British Gyreacta transmission, these devices produced only about 3 watt-hours per pound. Thus, energy density of the devices was even lower than that of available lead-acid batteries at the same discharge rate. However, certain characteristics of flywheels caused their use in preference to storage batteries, despite the problems then encountered in the use of flywheel structures. Firstly, the flywheel can be charged and discharged virtually an infinite number of times without degrading performance. Secondly, the flywheel can be charged at any reasonable rate. Thirdly, the flywheel can be discharged at any rate within the design limitations of ancillary equipment without degrading performance. These capabilities are largely responsible for the proposed use of flywheels in pollution-free urban vehicles. In most previous proposals, the rapid discharge capability of the flywheel has been primarily used to lend increased acceleration power to the vehicle in order to minimize the overall size of the main propulsion power plant. The present energy storage device provides a power plant of sufficient energy density to also enable its economic and practical use as the primary source in an urban vehicle.

SUMMARY OF THE INVENTION The invention primarily concerns a number of rotor structural configurations which form the major component of a high performance energy storage device. The several rotor configurations actually described herein, and those other configurations which follow from the description, are related in their use of high strength uniaxial filament-like materials to comprise the rotor structure. In particular, straight anisotropic filament or whisker materials are not only disposed substantially parallel to each other over the entire length of the rotor but are also substantially parallel to the major stress component acting on the rotor. Like any other flywheel device, the performances of the present rotor configurations are directly proportional to the specific strength of the material used in construction. By taking maximum advantage of the large specific strengths of filamentary materials, i.e., by aligning these filamentary materials substantially parallel to each other and to the major stress component which acts along the axis of each individual filament, a dramatic energy density increase in the total structure results, thus making a flywheel-type structure useful to a wide variety of applications beyond the capabilities of prior art rotary energy storage devices.

In the straight filament rotor configurations disclosed herein the low stresses which exist normal to the filaments are supported by a suitable matrix material or by a combination of a relatively few added filaments disposed normal to the principal filaments and potted in a suitable matrix material. For certain applications using high strength continuous filaments, such as ordinary music wire or boron filaments, a matrix is not required to maintain the filaments in alignment. In such a device, the filament bundle is secured in a central hub, which, when rotated, causes the filaments to fan out and align along respective force vectors generated by their own rotating masses. In such a configuration virtually all of the available strength of the material is effectively used at the maximum stress point (center of rotation).

In order to accommodate the extremely high rotational speeds of which the present device is capable, the performance limits of the bearings which support the rotating shaft must be maximized. Additionally, the rotating member must be maintained in a vacuum to reduce aerodynamic drag losses, thus presenting the necessity for a high-speed rotary seal or a passive magnetic coupling to drive the rotor through the wall of the vacuum chamber. Bearing and sealing functions can be provided through use of a combination of magnetic fluid seals, magnets, and bearings which allow operation of the rotating member under these conditions.

Accordingly, it is a primary object of the invention to provide a high power-density energy storage device which also has a high energy density capability.

It is another object of the invention to provide rotary structures capable of higher rotative speeds for higher energy outputs than have been previously available.

It is a further object of the invention to provide a rotor structure comprising substantially parallel high strength filamentary materials aligned along the major stress component acting on the structure.

Yet another object of the invention is to provide an energy storage device capable of operating at an abnormally high rotation speed with minimal aerodynamic and bearing drag losses.

A further object of the invention is to provide an energy storage device which can be readily and efficiently made from a large number of small autonomous rod-like components to minimize the likelihood of simultaneous failure of all components, thus maximizing the safety of the device.

It is also an object of the invention to provide a rotor structure having inherent gimballing capability about a stationary spin axis to minimize gyroscopic loads on the rotor and its spin bearings.

A still further object of the invention is to provide a safe, efficient, economical high performance and pollution-free energy storage device useful in an urban vehicle for alleviating the increasing contribution of motorized vehicles to noise and air pollution problems.

Additional objects, advantages, and uses of the invention will become apparent from the following detailed description of the preferred embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la, b, and c are enlarged perspective views of the sequential build-up of an embodiment of the invention, FIG. la showing a single, essentially uniaxial filament which forms the basic unit of the uniaxial strip of FIG. 1b, which strip in turn comprises the secondary structural unit of the composite bar of FIG. 10;

FIG. 2 is a perspective of a bar" rotor fabricated according to the invention;

FIG. 3 is a plan view of a rotating brush rotor fabricated according to the invention, the rotor being shown with filaments aligned along local stress vectors, the unspinning rotor being shown in phantom;

FIG. 4 is a schematic illustrating the fanning load operating on a point on a filament in a rotor constructed according to the invention;

FIG. 5a is a perspective of an optimized bar rotor fitted with an internal gimbal, a portion of the rotor being cut away to illustrate the increasing length of the filaments which are shown to be enlarged in the cut-away portion;

FIG. 5b is a cross section taken through the geometrical and mass center of the embodiment of the invention shown in FIG. 5a;

FIG. 6 is a section taken longitudinally through the optimized bar rotor shown in perspective in FIG. 5a;

FIG. 7a is an elevation of a disc rotor constructed according to the invention;

FIG. 7b is a plan view of the disc rotor of FIG. 7a;

FIGS. 8a and 8b are perspectives of wedge" rotors fabricated according to the invention, the rotor of FIG. 8b being fitted with a hub conforming to the cross sectional dimensions of said rotor;

FIGS. 9a, 9b, 9c, and 9d are schematics illustrating the relative drag of wedge rotors having varying half-angles as compared to the square block shown in FIG. 9a;

FIG. 10 is a partial section of an energy storage system useful with the present invention and having bearings within an associated vacuum can;

FIG. 11 is a perspective of a magnetic coupling device useful with the system shown in FIG. 10;

FIG. 12 is a partial section of an energy storage system useful with the present invention and having magnetic liquid seals which allow use of bearings disposed externally of an associated vacuum can;

FIG. 13 is a cross-section of a magnetic fluid bearing useful to prolong the charged life of the present invention;

FIG. 14 is a perspective of an internally gimballed multiple rotor energy storage device structured according to the invention; and,

FIGS. 15a and 15b are elevations of a portion of the device of FIG. 14, the device being shown in a precessed mode in FIG. 15b.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The performance, i.e., the stored kinetic energy of a rotating body, is directly proportional to the useable specific strength of the material used in the fabrication of the body.

Prior flywheels of optimum configuration composed of isotropic material such as solid steel have only a small fraction of useable strength to density compared with modern filamentary materials. A common uniaxial filamentary material, fine high-grade music wire, while not the most advantageous material for fabrication of the present rotor structure, has a useable specific strength of 1,500,000 lbs-in/lb, or about three times that of solid steel. A flywheel rotor configured to take maximum advantage of the anisotropic strength characteristics of uniaxial filamentary or whisker materials is capable of increased performance relative to flywheels composed of isotropic materials.

The term anisotropic" is generally defined as exhibiting properties with differing values when measured along axes taken in different directions. For the purposes of this disclosure, anisotropic is applied to a material to denote the property of strength along axes taken in different direction within the material. In particular, the term relates to a material having maximum strength along one particular axis thereof. For the filamentary materials or thin rods used in the present rotor structures, the axis of the material along which said material has maximum strength is the longitudinal axis of the material.

Considering the single filament or thin rod 10 shown in FIG. 1a to be spinning about its major axis, the specific energy of the filament 10 is given by:

E,,,=32.2!SA/W R i where:

E specific energy: foot-pounds per pound I moment of inertia: slug-ft S allowable stress: Ib/in A rod cross section: in

W= weight: lb

R one-half the spinning radius: ft or,

E,,,=32.2(IA/WR) (S/W) (2) As is the case with prior art flywheels composed of isotropic materials, it is apparent from Equation (2) that the specific energy of the filament I0 is also a function of the specific strength (8/ W) of the filament material. Similarly, the actual energy storage capability of a flywheel rotary device is given by Equation (1).

If the diameter of the filament 10 is infinitely small, the total stress in the filament is directed along its length, i.e., the direction of the centrifugal force acting on the filament 10, which, for the situation described, is the only force acting on the filament during rotation. If the filament 10 were the only element in a flywheel or rotating member, all of its allowable strength at its center contributes to the kinetic energy of this single element flywheel. If the effective shape of the filament 10 were optimized according to the principles described hereinafter for total rotor optimization, performance of the single filament rotor would be substantially increased.

In practice, the single filament 10 would have insufficient mass for most energy storage applications. However, FIGS. 1b and 1c illustrate the build-up of a flywheel rotary member according to the present invention. In FIG. lb, a plurality of single filaments 10 are aligned substantially parallel to each other to form a layered unidirectional strip 12. The width of the strip 12 is held to a low proportion of its length, such as l:I0 or 1:20 in order to minimize that force which acts to spread the filaments 10 apart due to the impossibility of aligning each filament 10 along the centrifugal force vector acting on the strip 12. Referring briefly to FIG. 4, the magnitude of the fanning load, L at a point P on a filament I0 will be L,= SR sin a 3 where S is the operating filament stress, R is the spinning radius of the point P where the fanning load is being determined, and a is the angle between the centerline of the strip 12 and a line connecting the center of rotation and the point of interest. Since sin a h/R, Equation (3) can be written:

L,= SR MR (4) L,= Sh 5) Thus, the magnitude of the fanning load on a given filament on the spinning strip 12 will be the same at any point on the filament.

The strips 12 are stacked to form a rotor bar 14 of a desired total weight and potential performance shown in FIG. 1c. The filaments 10 in the rotor bar 14 may be bonded together by a matrix 15 such as silicone rubber, epoxy, metal or a plastic or elastomeric material. The bar 14 in FIG. 10 is shown in the simple shape of a rectangular solid, although the bar shape may be optimized to provide greater energy storage capability, as will be described hereinafter. Optimization of the shape of each filament according to the principles described for optimization of the total bar rotor would yield increased performance but at a substantial increase in production cost and effort.

Referring to FIG. 2, a bar" rotor fabricated in essentially that fashion indicated for the bar 14 of FIG. 1c is shown. Straight, parallel, essentially uniaxial filaments 10 are bonded together in a matrix 22 of metal, plastic, or elastomeric material capable of supporting the fanning loads generated by the rotating mass of each filament 10. The matrix 22 may also bond to the rotor 20 one or more layers 24 of filaments having their axes disposed normal to the filaments 10. These layers 24 could be only one filament thick and could be regularly disposed throughout the rotor 20 to give additional resistance to fanning load stressing. However, the ratio of filaments in the layers 24 must remain low relative to the number of filaments 10 in order to maximize the useable strength of the filament material. The rotor 20 consisting of bonded filaments 10 in the simplified form of a rectangular solid is bonded within a rectangular, sleeve-like hub 26 composed of steel or other high strength material. The hub 26 has an integral shaft 28 comprised of upper and lower shaft members 30 which extend normal to and from the upper and lower major plane surfaces 32 of the hub 26, which surfaces 32 are substantially parallel to the filaments 10. The rotor 20 may be additionally secured within the hub 26 by means of an epoxy-type adhesive or by a high strength filler compound such as those materials used to form the matrix 22. On rotation of the bar" rotor 20, the principal load, F, on the rotor 20 is aligned along the longitudinal axis of the rotor, i.e., along and parallel to the filaments 10. Rotor spin-up and power takeoff is accomplished in a known fashion through the hub 26 and associated shaft 28. The use of certain continuous filamentary materials, such as music wire, boron filaments, etc., to form the rotor bar 14 do not require a matrix to maintain the filaments 10 in operative disposition. As shown in the brush rotor 16 in FIG. 3, the filaments 10a are allowed to fan out and align themselves with the local centrifugal force vector acting on each filament. As shown in phantom in FIG. 3, the loose filaments 10a are clamped together substantially tangentially between two rounded abutments 19 which form walls of a hub 18, which internally rounded walls are substantially parallel to the axis of 5 rotation of the rotor 16. The filaments 10a remain substantially parallel in a bar shape until rotation commences. On rotation of the rotor 16, the filaments 10a fan out symmetrically around the longitudinal axis of the rotor and line up precisely with the respective force vectors generated by their own rotating masses. The filaments 10a contacting that small portion of the perimeter of the abutments 19 holding the filaments when the rotor is at rest, fan out and virtually impress themselves against the full length of the perimeter of the abutments l9, i.e., assuming the shape of the abutments to be advantageously formed to approximate the shape assumed by the filaments under the operating conditions. The hub 18 could alternatively be cylindrical rather than the external rectangular solid shown in FIG. 3. In either event, the length of the hub 18, i.e., that dimension parallel to the longitudinal axis of the rotor 16, should be at least twice as great as the width or diameter of the hub. The strength degeneration of the filaments 10a caused by the moderate bending of each filament as it passes through the hub 18 is negligible.

lf music wire filaments having a useable specific strength of 1,500,000 lbs/in are utilized in the brush rotor 16, the energy storage capability is nearly twice that of a disc flywheel of optimized shape and constructed of isotropic steel such as is disclosed by Call in [1.8. Pat. No. 3,496,799. The energy storage capability of the brush rotor, though greater than the capabilities of previous flywheels, would be less than that of a theoretically optimized anisotropic disc due to the difference in effectiveness of the two configurations. A practical optimized disc configuration using anisotropic material will also be described hereinafter.

The actual energy storage capability of the brush rotor 16 and of the simple bar rotor 20 of FIG. 2 is given by Equation (1). By substituting appropriate values in Equation (1), it is seen that the brush" rotor 16 is capable of storing at least 16 watt-hours per pound, taking the usable strength of music wire to be about 70 percent of the tensile strength of the material (600,000 lbs/in). Such a value would apply to mechanical energy storage systems not subject to personnel hazard restrictions not exposed to more than a few thousand cycles of operation. Since factors other than specific strength of a material govern the specific energy content of a particular rotor configuration, the usable strength of a material will not always be the same proportion of the specific strength for all materials. If the bar rotor 20 were constructed of laminated high strength glass filaments and if appropriate allowances were made for personnel safety factors, handling degradation, static fatigue, cyclic fatigue, filament volume, and filament alignment, then the allowable strength could be as low as 25 percent of the tensile strength of the material. Even so, the glass filament bar rotor 20 would still have twice the specific energy capability of the music wire brush rotor 16 by virtue of its greater specific strength at the design condition.

The performance of the bar rotor 20 may be optimized in a fashion illustrated in FIGS. 5a and 6 so that the major stress component acting on the rotor is constant along its length. As seen in the drawings and particularly in the sectional view of FIG. 6, an optimized bar 34 has oppositely facing surfaces 35 and 37 defined by respective lines of rotation having an effective radius L and which are substantially mirror images across a longitudinal centerline of the bar 34. The surfaces 35 and 37 produced by the lines of rotation are characterized by a generally reverse curvature in the cross-sectional profile seen in FIG. 6, the surfaces being essentially convex near the center of rotation 39 of the bar 34 and sloping to a substantially concave shape near the ends 36 of the bar. Thus, the shape of the bar 34 is seen to generally decrease in thickness from a maximum at and around the center of rotation 39 to a minimum at the ends 36 of the bar. To achieve maximum rotor optimization, the thickness of the ends 36 would continuously diminish to infinity, thus practically producing a razor sharp edge. Practical considerations dictate forming the ends of the bar into a substantially square cut edge such as is shown at 41 in FIG. 6.

Generally, constant stressing of the bar is approximated when the cross-sectional thickness of the bar diminishes nonuniformly from a maximum thickness to a minimum thickness according to the relation y,,= one-half of the bar thickness at its center of rotation,

y =one-half of the bar thickness at any point on the surface of the bar, e the base of the natural system of logarithms, i.e.,

x= the spinning radius of the point k a numerical constant for a particular configuration Equation (6) yields a family of coordinates which explicitly defines the cross-sectional profile of the rotor 34 best shown in FIG. 6. The constant, k, in Equation (6) may be any real number. However, values of k greater than or less than 2.5 yield impractical rotor configurations. The rotor shaping yielded by Equation (6) can be practically approximated by either two cones joined at their bases and symmetrical across the axis of rotation or two regular pyramids joined at their bases (not shown). The rotor 34 could alternatively be shaped according to Equation (6) but having square or circular axial crosssections at any distance from the axis of rotation of the rotor.

This optimized bar 34 will yield at least 50 percent greater performance than the bar rotor. 20 described previously. The rotor 34 may be initially formed as a rectangular solid with straight, parallel filaments in the manner of the bar rotor 20 of FIG. 2. However, the rectangular bar is machined to the shape shown in FIGS. 50 and 6, thereby causing the filaments to have increasing length as is illustrated by enlarged filaments 10s shown in a cut-away portion of the rotor 34. The maximum load on the shorter filaments 10s at and near the center of rotation of the optimized bar 34 is distributed over a greater number of filaments which are not as heavily loaded as the full length filaments 102 shown enlarged at the ends of the rotor 34. Stated in another fashion, the short filaments 10s act to increase the load carrying capability of the longer center filaments Ie through additional shear load in the matrix. If each filament 10s and l0e of the rotor 34 were optimized in shape according to Equation (6), maximum performance optimization would be obtained.

The optimized bar 34 pictured in FIGS. a, 5b, and 6 also serves to illustrate an internal gimbal arrangement, shown generally at 38 in FIG. 5a and in section in FIG. 5b, which minimizes gyroscopic precession loads on the bearings used to hold the shaft supporting the bar 34 and on the rotating bar. In the bar configuration, the internal gimbal arrangement 38 described avoids the necessity for otherwise having large external gimbal rings and their associated bearings. More importantly, the rotor shaft does not have to be gimballed, enabling its output to be used directly. The gimbal arrangement 38 is seen to comprise a hollow box-like internal hub 40 which generally, assumes the shape of the rotor cross-section. The hub 40 is preferably constructed of steel or other high strength material. The optimized bar 34 is centered within the hub 40 and held therein by means of an elastic sleeve 42 disposed over that portion of the bars surface held within the hub. The elastic sleeve 42 is contiguous to the bar 34 on the inner surfaces of the sleeve and contiguous to the inner surfaces of the hub 40 on the outer surfaces of the sleeve to form a tight fitting within the hub 40. The sleeve 42 is made of elastic material in order to effect a better fit within the hub without inducing local stress concentrations. The sleeve 42 could well be fabricated from non-elastic material if this protection were not required in a particular application. As can be better seen in the sectional view in FIG. 5b, the hub 40 has two gimbal pins 44 extending from its opposite vertical faces, the pins 44 being aligned through the mass (and geometrical) center of the bar and hub combination. The pins 44 can be formed integrally with the hub 40 for increased structural strength.

A hollow box-like external hub 46 having four rectangular faces mountably encloses the bar 34 and hub 40 combination described above. The external hub 46 has two cylindrical recesses 48 disposed in and centered on its opposite vertical faces for receiving the gimbal pins 44. The pins 44 extend into the recesses 48 a sufficient distance to provide positive gimbal mounting of the bar 34 and hub 40 combination within the external hub 46. Anti-friction or elastomeric bearings (not shown) can be fitted into the recesses 48, if required. Stud shafts 50 extend from the opposite horizontal faces of the hub 46 and are aligned through the mass (and geometrical) center thereof. The hub 46 and shafts 50 are formed integrally with the hub and are made of steel or other easily worked high strength material. The gimbal limits of the bar 34 are determined primarily by the relative dimensions of said bar 34 and the external hub 46, particularly the clearance provided between the bar and hub and the length of the horizontal faces of the hub. For any foreseeable vehicle application wherein the flywheel is disposed therein with a vertical spin axis, reasonable gimbal limits are easily provided by the arrangement 38. The gimbal arrangement 38 is easily adapted to the brush and gimballing rotor 16 of FIG. 3 and to the bar rotor 20 of FIG. 2. Geometrical modification of the internal and external hubs 40 and 46 allows shaft attachment to and gimballing of the various rotor shapes and configurations which can be fabricated according to the invention.

The optimized bar 34, although capable of high energy storage capacity, is subject to aerodynamic drag losses directly proportional to the pressure and gas density within the vacuum can in which it is being rotated. For any given partial vacuum now practically maintainable torr), it can be shown that a disc shaped rotary member reduces drag losses by at least one order of magnitude, i.e., compared to a straight bar configuration having essentially the same diameter, volume, weight and rotary speed. The drag of the optimized bar is also about three times less than the straight bar, but must be operated at a higher speed to achieve its greater performance. Additionally, the volume of the vacuum can enclosing the disc-type rotor is substantially smaller than is possible for a non-optimized bar rotor.

A disc rotor 52 fabricated according to the present invention is shown in FIGS. 7a and 71;. The shape of the disc rotor 52 is coincidentally similar to that disclosed by Call in US. Pat. No. 3,496,799. Call provides a disc flywheel composed of isotropic material with an optimized generally lenticular shape which produces a substantially uniform stress throughout the flywheel mass during rotation.

The disc rotor 52 is seen to progressively decrease in thickness from a maximum at and around the hub or center of rotation 54 to a minimum at the circumferential tip 60. This configuration is built up by bonding together a plurality of the unidirectional strips 12 previously shown in FIG. 1b.

The strips 12 are stacked in an offset sequence, the geometrical center of each rectangular strip 12 being coincident with the center of rotation 54 of the rotor 52. The strips 12 may be initially stacked into a rectangular solid with the four edges of each strip 12 being aligned with the edges of the other strips 12, the resulting structure then being fanned out" by offsetting each said strip 12 a finite angular distance from the immediately adjacent strips 12. By continuing the relative angular offset of adjacent strips 12 around a full 360 angle, the geometrical relationship shown in FIG. 7b is produced. The strips 12 are then bonded into a matrix to maintain them at the proper angular offset. As an idealized and simplified example, if the rotor 52 were comprised of twelve of the strips 12, then each strip 12 would be fanned out from thealigned rectangular solid described above at an angle of 30 relative to the adjacent strips 12 in the rotor 52, thereby forming a discshaped member having maximum thickness at or around the center of rotation 54 and minimum thickness at the circumferential tip 60. At the center of rotation 54 the thickness of the rotor 52 is comprised of a finite contribution from each of the strips 12 comprising the rotor. At the circumferential tip 60, the thickness is comprised of the finite contribution of a relatively smaller portion of the strips 12, thereby yielding a differential thickness which results in the generally lenticular shape shown in FIG. 7a. The filaments comprising the strips 12 are substantially aligned within the rotor 52 with the local centrifugal force vector acting on each filament, thereby providing an energy storage capacity consistent with the maximum useable specific strength of the filaments themselves. I-Iub mounting means (not shown) for power takeoff and flywheel spin-up may be provided by bonding metal hubs to either side of the hub or center of rotation 54.

A bi-directional fanning of the strips 12 produces a wedge rotor 62 shown in FIG. 8a. The aerodynamic drag on the rotor 62 can be shown to be about equal to the drag acting on the optimized disc rotor 52. However, the advantage of the wedge configuration is that its straighter filaments are more nearly lined up with the radial force vector. Although a vacuum can surrounding the disc" rotor 52 can be made smaller than that required for the wedge" rotor 62, all of the uniaxial filaments comprising the wedge rotor can be straight and aligned virtually parallel to the local centrifugal stress vector acting on each filament. The wedge" rotor 62 is seen to result from a buildup of the unidirectional strips 12, one of the strips 12 being at first slightly and regularly offset relative to the next lower strip 12 in a counterclockwise direction, and the strip build-up then being reversed to a clockwise direction.

Aerodynamic drag acting on the wedge rotor 62 depends on the slope of the surface of the strips 12, i.e., the magnitude of the relative offset between said strips 12. This factor is more easily discussed by consideration of the half-angle between the line defining the fanning surface and a line normal to the axis of rotation through the wedge caused by the reversal in strip buildup. As seen in FIGS. 9a, 9b, 9c, and 9d, drag varies significantly in proportion to the half-angles shown taken through the cross-sections of several representative wedge shapes. Assuming the rectangular body 64 of FIG. 9a to have a normalized drag of 100 percent, the wedge rotor of FIG. 9b, having a half-angle of 1429, exhibits a relative drag of 10.5 percent. Progression to lower half-angles produces reduced drag, but eventually produces dimension problems of greater severity, since the filaments tend to separate tangentially when elongated under the radial stress vector.

FIG. 8b illustrates a wedge rotor 62ahaving a hub 40a shaped to accommodate the wedge shape of the rotor in the manner indicated hereinabove.

For purposes of illustration, FIG. shows a state-of-the art energy storage system 65 capable of use with the present energy storage device. The disc" rotor 52 is shown in this view as the energy storage device, but, with alteration of the shape of certain components of the system 65, any configuration of the present energy storage device may be used in the system. The system 65 comprises a hermetically sealed vacuum can 66 which generally follows the shape of the rotor 52 except near the axis of rotation 68 of said rotor where the can 66 is provided with integral cylindrical extensions 70 and 72. The extensions 70 and 72 both accommodate dry bearings 74 and respectively accommodate a plate 76a of a magnetic coupler 76 and a magnetic suspension device 78. The bearings 74 are burnished with MoS or other suitable dry lubricant, and function without additional lubrication in the vacuum environment within the can 66. The dry bearings 74 are completely unloaded for the static situation by the permanent magnetic suspension device 78 and are only loaded in a dynamic operating environment, such as in a vehicle. Low vapor pressure lubricating oils can also be used at these modest vacuum pressures. However, if the system 65 is installed in a vehicle with the spin axis vertical, then x and y axis gimbals 80 and 82 act to relieve gyroscopic precessional loads caused by pitching and turning of the vehicle. Operation of the flywheel with the system 65 thus disposed does not effect vehicle turning, nor does vehicle turning affect the flywheel, since the vehicle turns around the spin axis of the rotor 52.

The rotor 52 is mounted on a two-piece shaft 84 coinciding with the spin axis of the rotor. The shaft 84 is journaled at each end in the bearings 74 and tenninates at its upper end at the plate 76a of the magnetic coupler 76 and at its lower end at permanent magnet 78a of the magnetic suspension device 78. Plate 76b of the magnetic coupler 76 is disposed outside of the vacuum can 66, the plate 76b being driven in this instance by an electric motor 86, said plate 76b, in turn, driving the plate 76a which spins the rotor 54 without direct connection through a non-magnetic portion of the vacuum can 66. By utilizing such an indirect drive system, high speed rotating seals are not required; thus the operating pressure inside the vacuum can may be held lower than might otherwise be possible.

The magnetic coupler 76 is shown in greater detail in FIG. II. The coupler 76 comprises the two plates 76a and 76b which each consist of a multipole magnet 88 and an iron backing 90, the backing 90 of the plate 760 being attached to the shaft 84 and the backing 90 of the plate 76b being joined.

to a shaft member 92 coupled to the electric motor 86. The present energy storage device, because of its high speed and low torque characteristics, is especially suited for use with the coupler 76. Since the magnetic coupler 76 is not novel and is well-known in the art, further description thereof is not given herein. However, it should be noted that, despite the advantages of a hermetically sealed vacuum can and the improved vacuum condition thus made possible, the coupler 76 has the relative disadvantage of losing lock between the plates 76a and 76b if design torque is exceeded, and will not relock without a full restart.

Returning to FIG. 10 and the system 65 the vacuum can 66 is provided with a safety ring 94 and a gimbal frame 96. A shock absorbing suspension 98 stabilizes the system 65. If the internal gimballing arrangement 38 of FIGS. 5 and 6 is used with an aptly sized vacuum can, the external gimbals and 82 may not prove necessary for most applications. In the system shown, compensation for precession resulting from the earths rotation can be provided either in the form of springs, slight friction, or by locating the gimbal axes slightly above the swung center of gravity, so that the system 65 will be self-compensating.

Spin-up of the rotor 52 is accomplished as described previously. Power take-off is similarly accomplished. In this instance, the electric motor 86 becomes a generator converting mechanical energy to electrical energy for efficient conduction to electric motors, such as at the wheels of a vehicle. Power take-off can just as easily be accomplished by means of hydraulic motors and pumps, or an all mechanical system could also serve in place of the electric motor 86.

Certain applications are better accomplished by using a turbine or internal combustion engine (with an over-riding clutch) as the driving motor. In the hybrid installations the engines could be much smaller than usual, since the flywheel would provide all of the extra power required for acceleration of the vehicle. Using the instant concept, the flywheel in such a hybrid vehicle would only weigh about 1 percent of the vehicle weight. At a can pressure of 10: torr, the rotor 54 could be run for several days despite bearing losses. By comparison, the useable power for the flywheel used in the Oerlikon bus was diminished in a few hours.

The safety hazard of the present energy storage device is minimized relative to conventional flywheels since the present structure comprises a large number of relatively small highly stressed components. A rotor having a total energy content of 25,000,000 ft-Ibs, would constitute a formidable hazard if it were fabricated of a single piece of isotropic material and were to fail at the rated speed. However, fabrication of the present rotor 52 from music wire strands 0.003 inch in diameter would result in a kinetic energy on a single strand of wire of only 1 to 2 ft-lbs. In any conceivable rotor configuration, the matrix strength will be only a small percentage of the strength of the filamentary material, thus resulting in a relatively progressive failure, rather than the instantaneous failure occuring with single-piece flywheels.

The high rate of rotation possible with the present energy storage device results in low torque, since the torque varies indirectly with the rotation speed of the flywheel for a given power level. For example, an embodiment of the present energy storage device capable of producing 50 horsepower at 35,000 rpm would exert a torque of only 7.5 ft-lbs. For the music wire rotor 52 described above, the torque exerted on each wire would be only 3 X 10' ft-lbs. The low torque would have a negligible effect on the rotor as well as on a vehicle in which the rotor could be used.

The most significant factor governing the performance of the present energy storage device is the usable specific strength of the filamentary or whisker material used in its construction. Presently available wire material is in almost every instance stronger along its length than the parent material in bulk form. Steel wire is available having a tensile strength of 600,000 lbs/in. Other wire material, such as beryllium wire, actually exceeds the specific strength of steel wire. More exotic filamentary and whisker material now available includes fiberglass, graphite, boron, tungsten-carbide, etc. These available materials have been developed because of the need for high strength, high temperature, and, usually, lightweight materials. However, the present use requires only the high specific strength characteristic, since the high temperature capability is not required.

Most filamentary and whisker materials described, unlike the wire materials, must be bonded into a suitable matrix. The matrix material can be the epoxy or polyester resins or metals, such as aluminum and magnesium. However, in the high vacuum environment necessary for efficient operation of the present device, a matrix material relatively free of out-gassing is required to avoid degrading the vacuum. Protection of a normally out-gassing matrix with a thin layer of vacuum deposited metal or other low vapor pressure material is found to be useful.

Unlike any battery, the performance of the present energy storage device is virtually unaffected by the number of charge/recharge cycles, the ambient temperature, or by the rate of charge or discharge. The efficiency of energy storage is virtually 100 percent, since the only losses are the aerodynamic losses on the spinning rotor in the vacuum environment and the losses resulting from bearing drag, which should be minimal at the zero loading of the magnetic suspension. The overall efficiency of an energy storage system using the present device is substantially greater than the efficiency of batteries, presently available flywheel systems, or any other known energy storage system.

An energy storage system configuration which utilizes the present energy storage device and which'overcomes certain disadvantages of the system 65 described hereinabove is shown in FIG. 12. The system shown is seen to utilize an optimized bar 3411 spinning in a vacuum environment maintained by a vacuum can 100 having flared ends defined by the gimbal limits of the bar 34a. The bar 34a is gimballed internally in the same fashion previously described for the bar 34 of FIGS. a and 5b. In this system configuration, shaft members 50a actually pass through openings 108 and 110 in the upper and lower portions of the can 100, the openings 108 and 110 being circular and having their centers coincident with the axis of rotation of the bar 34a. Magnetic fluid seals 112, such as those described by Rosensweig in U.S. Pat. No. 3,215,572, allow operation of the bar 34a at the necessary vacuum within the can 100. The seals 112 provide sealing between the internal vacuum in the can 100 and ambient air with virtually no leakage (less than cm/sec). The seals 112 not only permit rotation in a low drag environment, but also allow the placement of bearings externally of the vacuum can 100, where available high speed bearings and conventional high speed lubrication may be used.

Since there is no solid contact between the seal 112 and the rotating shaft, the contribution of the seal to the overall drag is extremely low and can actually be calculated according to:

P (qr/4) 1; N (878) D (9 1 where:

1 viscosity of seal fluid: poise N= Number of stages D Diameter: cm

to Rotating speed: rad/sec 8 seal gap seal width P= Drag: dyne-cm/sec Referring again to FIG. 12, high speed bearings 124 are disposed externally of the vacuum can 100. Since the drive shaft i.e., the lower shaft member 50a also extends externally of the can 100, rotor spin-up and power take-off is accomplished in a more direct fashion than is possible with the system 65 of FIG. 10. Loading on the bearings 124 is minimized to reduce bearing drag by providing complete gravity unloading of said bearings through the use of a passive magnetic suspension 126. The magnetic suspension 126 accommodates only the static load situation, the dynamic loads being accommodated by the conventional bearings 124.

FIG. 13 illustrates the general concept underlying an unconventional bearing 128 which can be expected to exhibit reduced drag loss capability and have a virtually infinite operating life. The bearing 128 is completely passive and avoids solid contact between any moving parts. The bearing 128 generally provides stability in three planes through the use of a permanent annular ring magnet 130. The magnet 130 provides stability in two planes, while stability in the third plane is provided by a fluid 132, such as air sealed by magnetic fluid which is trapped by the magnetic field of the magnet 130. An

arrangement of concentric magnetic fluid seals shown at 134 similar to the seal 112 previously described assists in entrapment ofthe fluid 132.

The bearing 128 may be used in the system of FIG. 12 with the conventional high speed bearings 124 primarily to obtain lower drag loss in the static loading condition to minimize rotor run-down time. The bearing 128 shown is seen to have an annular plate 136 formed integrally with a rotating shaft 138, which shaft 138 also provides the shaft support for the spinning rotor and serves for rotor spin-up and power take off. The plate 136, composed of magnetizable material, has an annular depression 140 formed in one face thereof and defined by two raised concentric beveled ridges 142. Opposing the ridges 142 and held fixedly at a finite distance therefrom are concentric annular pole pieces 144 held in spaced relation by and contiguous to the annular ring magnet 130. The magnet and pole piece 144 combination is fixedly attached to a stationary support 148 and surrounds a portion of the rotating shaft 138. A ferromagnetic fluid 150, which comprises the concentric fluid seals 134, is held magnetically in the finite space between the ridges 142 and beveled edges 152 of the pole pieces 144, thus sealing a chamber 154 defined by the ridges 142 and edges 152. This sealing function is accomplished in the same fashion as that described for the seal 112 of FIG. 12. The chamber 154 is reduced in volume by the provision of non-magnetic filler members 156 on either side of the chamber 154. The structure described thus produces a reduced chamber 154 which holds the previously mentioned fluid 132. The fluid 132 within the chamber 154 is trapped and held at moderate pressures for indefinite periods. An operable bearing 128 typically seals a 0.005-inch gap of air at pressures near 3 psi within the chamber 154. Provision of a plurality of chambers allows scalable staging of the bearing 128 to a desired loading capability. The bearings 128 are usually arranged in opposing pairs in order to conveniently maintain axial stability.

FIG. 14 depicts a multiple rotor energy storage device 200 which combines a number of advantageous features of the present invention. The device 200 is seen to comprise a plurality of optimized cylindrical rotors 202 individually gimballed on an enlarged portion 203 of a rotary shaft 204 according to the internal gimbal arrangement previously shown in FIGS. 5a and 5b. Each rotor 202 is constructed according to the invention, being composed of a large number of filaments having their respective longitudinal axes disposed parallel to the longitudinal axis of the rotor. The rotors 202, as shown, are cylindrical in cross section, having a greater diameter at and near the center of the rotor and tapering symmetrically to reduced end portions 206. It should be understood that the rotors 202 could take shapes other than the tapering cylindrical form shown, the cylindrical shape being used mainly for illustrative purposes.

The rotors 202, as better seen in FIGS. 15a and 15b, are individually gimballed on the shaft 204. Each rotor 202 has an internal hub 208 comprising a hollow cylinder 210 which receives the rotor through an axial opening 212 in the cylinder 210. Each rotor 202 is preferably held within the cylinders 210 by means of an elastic sleeve 214 disposed over that portion of the rotors surface held within the cylinder, i.e., in the fashion previously described for the embodiment of the invention shown in FIGS. 5a and 5b. Each rotor and hub combination is centered within one of a number of substantially oval shaped ports 216 regularly disposed in the enlarged portion 203 of the shaft 204. The ports 216 are interdigitated along the length of the portion 203. Thus, if the rotors 202 were numbered along the shaft 204, those rotors occupying evennumbered positions would be mutually parallel. Similarly, those rotors 202 occupying odd-numbered positions would be mutually parallel. Any oddnumbered rotor would be spatially perpendicular to any even-numbered rotor.

Each cylinder 210 has two gimbal pins 218 extending from diametrically opposite points thereon, the pins 218 being aligned through the mass (and geometrical) center of the rotor and hub combination. The pins 218 are rotatably received within recesses 220 disposed in the shaft 204, two each of the recesses 220 being aligned and centered on opposite sides of each of the ports 216. The longitudinal axis of each pair of aligned recesses 220 is perpendicular to the longitudinal axis of the ports 216. As is clearly seen in FIG. 150, the ports 216 may have portions of their volume shared with the perpendicular ports 216 on either side thereof. Although this space sharing arrangement is not necessary, it does allow the most compact positioning of rotors 202 per unit length of shaft 204.

FIG. 15b illustrates the degree of freedom allowed by the internal gimbal arrangement, the magnitude of this motion being dependent on the design parameters desired for a particular application. Using the device 200 shown, the shaft 204 need not be externally gimbaled to avoid precessional loading. Of course, the device 200 could be constructed without the internal gimballing feature, i.e., each rotor 202 could be fixed on the shaft 204.. In such an event, the shaft itself would then be externally gimbaled. The structure of the device 200 also allows provision of a useful safety feature. If one of the rotors 202 were longer than the remaining rotors, the longer rotor would fail prior to the attainment of the design limitations of the device 200 itself. That is, the stresses on the longer rotor under a certain set of operating conditions are greater, thus maximizing the probability of a relatively safe failure of this single rotor rather than the substantially simultaneous failure of a number of the rotors. The failure of the longer rotor, or of any individual rotor, signals shutdown of the device 200 to prevent further failure. In any event, failure of several of the rotors 202 is an unlikely occurrence, the device 200 being substantially more safe at rotation rates approaching design limitations than the other embodiments of the invention described herein.

Uses of the present energy storage device too numerous to mention are possible. Rotor configurations other than those explicitly described but which embody the uniaxial, anisotropic filaments disposed substantially parallel to each other and to the major stress component acting on the filaments are also possible. Thus, the invention may be practiced in fashions other than that specifically outlined herein without departing from the invention as defined by the following claims.

lclaim:

1. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising,

a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other;

matrix means for bonding the members together; and,

a coating of low-vapor pressure material disposed over the surface of the structure.

2. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of straight anisotropic filament-like members, said members being formed into strips, the members within any given strip being parallel, and wherein the strips are disposed within the structure at an angle with respect to certain other strips of parallel members.

3. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising,

a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other; and wherein the members are formed into a substantially rectangular unit having a length at least ten times greater than its width.

4. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising,

a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other;

and wherein the members are formed substantially into a cylindrical unit of a length at least ten times greater than its diameter.

5. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising,

a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other;

and wherein said structure has a symmetrical cross-sectional profile defined by opposed surfaces about the axis or rotation,

said structure having a relatively thick center portion around said axis and relatively thin end portions, said surfaces of said profile each having the shape of an exponential curve and being symmetrical about a plane extending through the geometrical center of the structure and perpendicular to the axis of rotation.

6. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising,

a plurality of straight anisotropic filament-like members, the longitudinal axis of said members being disposed parallel to each other;

and wherein said structure is symmetrically contoured in cross-section about said axis of rotation and has a center portion of maximum thickness around said axis and end portions of minimum thickness at the end portions,

the center portion of the structure having a cross-sectional thickness diminishing non-uniformly from said maximum to said minimum according to the relation:

9 o wherein; I

l t i is of the Stluctule at the axis Of otation y one-half of the thickness of the structure at any point on the surface of the structure e the base of the natural system of logarithms x a spinning radius of a point on the surface of the structure k a numerical constant.

7. The energy storage structure of claim 6 wherein k is in the range of numerical values between 2.5 and 100.

8. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising,

a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other; and wherein each member is shaped according to the relation:

y, one-half of the thickness of the structure at the axis of rotation y one-half of the thickness of the structure at any point on the surface of the structure e the base of the natural system of logarithms x a spinning radius of a point on the surface of the structure k a numerical constant.

9. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of initially straight anisotropic filamentlike members having maximum strengthto-density along their longitudinal axes, said members being oriented within said structure with the longitudinal axis of each member disposed substantially parallel to the longitudinal axis of the structure, said structure further comprising,

hub means for holding the members at their centers of rotation, rotation of the structure causing the members to fan out, each said member aligning substantially along the local principal stress vector acting thereon.

10. The energy storage structure of claim 9 wherein the members are initially formed substantially into a rectangular unit having a length at least ten times greater than its width.

11. The energy storage structure of claim 9 wherein the members are initially formed substantially into a cylindrical unit having a longitudinal dimension at least 10 times greater than its diameter.

12. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of anisotropic filament-like members, said members being formed into strips, the members within any given strip being parallel, and wherein the strips are formed into a generally disc shape comprising two opposing surfaces and a circular peripheral edge, the structure being symmetrically contoured in cross-section about said axis of rotation, and having a center portion of maximum thickness and edge portions of minimum thickness.

13. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of anisotropic filament-like members, the structure being formed into a generally disc shape,

a multiplicity of the members being bonded together into flat strips and having the longitudinal axis of each member oriented therein substantially parallel to adjacent members,

the strips further extending through and perpendicular to the axis of rotation and being bonded together in a regularly offset angular relation to each other whereby each strip contacts at least one other strip on at least one of its surfaces.

14. The energy storage structure of claim 13 wherein adjacent strips are maintained in contacting relation with each other over major portions of their surfaces.

15. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of essentially anisotropic filament-like members having maximum strength-to-density along their longitudinal axes,

the members being bonded together into a plurality of essentially fiat strips and having the longitudinal axis of each member oriented therein substantially parallel to the longitudinal axis of the strip, the strips extending through and perpendicular to the axis of rotation and progressively and successively surmounting each other and being built-up and bonded together in a regularly offset angular relation to each other with certain of said strips extending in a counterclockwise direction and certain other of said strips extending in a clockwise direction.

16. In an energy storage system a rotatable shaft,

an energy storage structure having its midpoint mounted for tilting movement on the shaft and having an axis of rotation coincident with the axis of rotation of the shaft when the longitudinal axis of a cross-section taken through the structure is perpendicular to the shaft,

said structure comprising a plurality of anisotropic filamentlike members having maximum strength-to-density along their longitudinal axes.

17. The energy storage system of claim 16 wherein the filament-like members are oriented within the energy storage structure with the longitudinal axis of each said member disposed along a principal stress vector acting on the filament during rotation of the structure.

18. An energy storage structure rotatable about an axis extending transversely therethrough, comprising,

a multiplicity of anisotropic filaments having maximum strength-to-density along their respective longitudinal axes, the filaments being oriented within said structure with the longitudinal axis of each said filament disposed along the vector summation of the principal forces acting on the filament during rotation of the structure.

19. The energy storage structure recited in claim 18, including means engaging the structure at its midpoint and mounting said structure for rotation about said axis.

20. In an energy storage system,

a shaft rotatable around a stationary axis, and

a plurality of energy storage rotary structures mounted on the shaft, and having axes of rotation coincident with the axis of rotation of the shaft when the longitudinal axes of respective cross-sections taken through the structures are perpendicular to the shaft, each of said structures comprising a plurality of straight,

filament-like members, said members being oriented within each structure with their longitudinal axes disposed substantially parallel to the longitudinal axis of a section of the rotary structure taken parallel to the member.

21. The energy storage system of claim 20 and further comprising hub means on each of the rotary structures, and pin gimballing means on each of said hub means,

the shaft having a plurality of ports for receiving one each of said rotary structures therethrough and a plurality of recesses perpendicular to, aligned with and communicating with each of said ports for receiving said pin gimballing means, the rotary structures being capable of pivotal displacement around said gimballing means to relieve precessional loading on the shaft.

22. In an energy storage system, a rotatable shaft and,

an energy storage structure having its midpoint mounted for tilting movement on the shaft and having an axis of rotation coincident with the axis of rotation of the shaft when the longitudinal axis of a cross-section taken through the structure is perpendicular to the shaft,

said structure comprising a plurality of anisotropic filamentlike members oriented with their longitudinal axes parallel to each other.

23. The energy storage system of claim 22 and further comprising,

intemal hub means on the said structure,

pin gimbaling means on said internal hub means, and

external hub means formed with the shaft for receiving the energy storage structure therethrough, said external hub means having recesses therein for receiving said pin gimballing means, the energy storage structure being capable of pivotal displacement around said gimballing means to relieve precessional loading on the shaft.

24. The energy storage system of claim 23 and further comprising an elastic sleeve disposed around the said structure and between said structure and said internal hub means.

25. An energy storage structure comprising a plurality of anisotropic filament-like members rotatable about an axis extending transversely therethrough,

said structure having a generally wedge-like cross-section with wedge-shaped leading and trailing surfaces,

the structure being symmetrical about a plane extending through the geometrical center of said structure perpendicular to the axis of rotation.

26. An energy storage structure rotatable about an axis extending transversely therethrough, comprising,

a plurality of anisotropic filament-like members arranged with their longitudinal axes parallel, and

hub means including arcuately shaped spaced walls,

said hub means engaging said members with the mid-portions of said walls in engagement with the mid-portions of said members,

the members fanning out on rotation of the structure whereby the portions of said members within said hub means will bear against said walls and be supported thereby. 

1. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising, a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other; matrix means for bonding the members together; and, a coating of low-vapor pressure material Disposed over the surface of the structure.
 2. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of straight anisotropic filament-like members, said members being formed into strips, the members within any given strip being parallel, and wherein the strips are disposed within the structure at an angle with respect to certain other strips of parallel members.
 3. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising, a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other; and wherein the members are formed into a substantially rectangular unit having a length at least ten times greater than its width.
 4. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising, a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other; and wherein the members are formed substantially into a cylindrical unit of a length at least ten times greater than its diameter.
 5. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising, a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other; and wherein said structure has a symmetrical cross-sectional profile defined by opposed surfaces about the axis or rotation, said structure having a relatively thick center portion around said axis and relatively thin end portions, said surfaces of said profile each having the shape of an exponential curve and being symmetrical about a plane extending through the geometrical center of the structure and perpendicular to the axis of rotation.
 6. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising, a plurality of straight anisotropic filament-like members, the longitudinal axis of said members being disposed parallel to each other; and wherein said structure is symmetrically contoured in cross-section about said axis of rotation and has a center portion of maximum thickness around said axis and end portions of minimum thickness at the end portions, the center portion of the structure having a cross-sectional thickness diminishing non-uniformly from said maximum to said minimum according to the relation: y yoe kx wherein: yo one-half of the thickness of the structure at the axis of rotation y one-half of the thickness of the structure at any point on the surface of the structure e the base of the natural system of logarithms x a spinning radius of a point on the surface of the structure k a numerical constant.
 7. The energy storage structure of claim 6 wherein k is in the range of numerical values between 2.5 and
 100. 8. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, comprising, a plurality of straight anisotropic filament-like members, the longitudinal axes of said members being disposed parallel to each other; and wherein each member is shaped according to the relation: y yoe kx wherein: yo one-half of the thickness of the structure at the axis of rotation y one-half of the thickness of the structure at any point on the surface of the structure e the base of the natural system of logarithms x a spinning radius of a point on the surface of the structure k a numerical constant.
 9. An energy storage structure rotatable about an axis of rotation extending transversely therethrouGh, the structure comprising a plurality of initially straight anisotropic filament-like members having maximum strength-to-density along their longitudinal axes, said members being oriented within said structure with the longitudinal axis of each member disposed substantially parallel to the longitudinal axis of the structure, said structure further comprising, hub means for holding the members at their centers of rotation, rotation of the structure causing the members to fan out, each said member aligning substantially along the local principal stress vector acting thereon.
 10. The energy storage structure of claim 9 wherein the members are initially formed substantially into a rectangular unit having a length at least ten times greater than its width.
 11. The energy storage structure of claim 9 wherein the members are initially formed substantially into a cylindrical unit having a longitudinal dimension at least 10 times greater than its diameter.
 12. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of anisotropic filament-like members, said members being formed into strips, the members within any given strip being parallel, and wherein the strips are formed into a generally disc shape comprising two opposing surfaces and a circular peripheral edge, the structure being symmetrically contoured in cross-section about said axis of rotation, and having a center portion of maximum thickness and edge portions of minimum thickness.
 13. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of anisotropic filament-like members, the structure being formed into a generally disc shape, a multiplicity of the members being bonded together into flat strips and having the longitudinal axis of each member oriented therein substantially parallel to adjacent members, the strips further extending through and perpendicular to the axis of rotation and being bonded together in a regularly offset angular relation to each other whereby each strip contacts at least one other strip on at least one of its surfaces.
 14. The energy storage structure of claim 13 wherein adjacent strips are maintained in contacting relation with each other over major portions of their surfaces.
 15. An energy storage structure rotatable about an axis of rotation extending transversely therethrough, the structure comprising a plurality of essentially anisotropic filament-like members having maximum strength-to-density along their longitudinal axes, the members being bonded together into a plurality of essentially flat strips and having the longitudinal axis of each member oriented therein substantially parallel to the longitudinal axis of the strip, the strips extending through and perpendicular to the axis of rotation and progressively and successively surmounting each other and being built-up and bonded together in a regularly offset angular relation to each other with certain of said strips extending in a counterclockwise direction and certain other of said strips extending in a clockwise direction.
 16. In an energy storage system a rotatable shaft, an energy storage structure having its midpoint mounted for tilting movement on the shaft and having an axis of rotation coincident with the axis of rotation of the shaft when the longitudinal axis of a cross-section taken through the structure is perpendicular to the shaft, said structure comprising a plurality of anisotropic filament-like members having maximum strength-to-density along their longitudinal axes.
 17. The energy storage system of claim 16 wherein the filament-like members are oriented within the energy storage structure with the longitudinal axis of each said member disposed along a principal stress vector acting on the filament during rotation of the structure.
 18. An energy storage structure rotatable about an axis exteNding transversely therethrough, comprising, a multiplicity of anisotropic filaments having maximum strength-to-density along their respective longitudinal axes, the filaments being oriented within said structure with the longitudinal axis of each said filament disposed along the vector summation of the principal forces acting on the filament during rotation of the structure.
 19. The energy storage structure recited in claim 18, including means engaging the structure at its midpoint and mounting said structure for rotation about said axis.
 20. In an energy storage system, a shaft rotatable around a stationary axis, and a plurality of energy storage rotary structures mounted on the shaft, and having axes of rotation coincident with the axis of rotation of the shaft when the longitudinal axes of respective cross-sections taken through the structures are perpendicular to the shaft, each of said structures comprising a plurality of straight, filament-like members, said members being oriented within each structure with their longitudinal axes disposed substantially parallel to the longitudinal axis of a section of the rotary structure taken parallel to the member.
 21. The energy storage system of claim 20 and further comprising hub means on each of the rotary structures, and pin gimballing means on each of said hub means, the shaft having a plurality of ports for receiving one each of said rotary structures therethrough and a plurality of recesses perpendicular to, aligned with and communicating with each of said ports for receiving said pin gimballing means, the rotary structures being capable of pivotal displacement around said gimballing means to relieve precessional loading on the shaft.
 22. In an energy storage system, a rotatable shaft and, an energy storage structure having its midpoint mounted for tilting movement on the shaft and having an axis of rotation coincident with the axis of rotation of the shaft when the longitudinal axis of a cross-section taken through the structure is perpendicular to the shaft, said structure comprising a plurality of anisotropic filament-like members oriented with their longitudinal axes parallel to each other.
 23. The energy storage system of claim 22 and further comprising, internal hub means on the said structure, pin gimbaling means on said internal hub means, and external hub means formed with the shaft for receiving the energy storage structure therethrough, said external hub means having recesses therein for receiving said pin gimballing means, the energy storage structure being capable of pivotal displacement around said gimballing means to relieve precessional loading on the shaft.
 24. The energy storage system of claim 23 and further comprising an elastic sleeve disposed around the said structure and between said structure and said internal hub means.
 25. An energy storage structure comprising a plurality of anisotropic filament-like members rotatable about an axis extending transversely therethrough, said structure having a generally wedge-like cross-section with wedge-shaped leading and trailing surfaces, the structure being symmetrical about a plane extending through the geometrical center of said structure perpendicular to the axis of rotation.
 26. An energy storage structure rotatable about an axis extending transversely therethrough, comprising, a plurality of anisotropic filament-like members arranged with their longitudinal axes parallel, and hub means including arcuately shaped spaced walls, said hub means engaging said members with the mid-portions of said walls in engagement with the mid-portions of said members, the members fanning out on rotation of the structure whereby the portions of said members within said hub means will bear against said walls and be supported thereby. 